The invention relates to a method, of and plot generator for selecting angle, range and target azimuth extent data produced for targets and stored in a register. The generator comprises a video processor for generating the data on the reception of sensor signal data. The invention further relates to a radar system comprising such a plot generator or operating in accordance with said method. The angle, range and target azimuth extent data is hereafter frequently referred to as plot data, where the target azimuth extent is a measure for the reflective power of the target derived from the number of return signals obtained in successive radar scans.
The above plot generator is particularly useful in track-while-scan radar systems for air space surveillance, where in successive radar scans the return signals are correlated in range and, on the basis of the plot data then obtained per target and per antenna revolution, track parameters are generated. This requires the storage of return signal data of several successive radar scans in a memory. It is therefore of advantage to use a digital plot generator.
In order not to overload the central processor, which is necessary to calculate the track parameters, and to avoid long reaction times, incurred with the calculation of a certain false-track probability, the supply of plot data has to be strongly reduced. A large supply of plot data also influences the system's usability adversely. Hence, a selective supply of plot data is desirable. Important selection methods for this purpose rest in the first instance on the principle of the suppression of clutter, noise and return signals from fixed targets. Despite this, with the presence of large flocks of birds the number of plots generated increases to excess with all its consequences. However, the means applied in practice, such as sensitivity time control (STC) and circular polarisations in the existing radar systems, are not adaptive, that is they are not dynamic and unsuitable for adaptation to changes in weather, sea state and ambient conditions. The provision of a more powerful STC in the radar system does not give the desired solution either, because a reduction in the number of passed return signals from birds is associated with a significant decrease of the plot detection probability.